The Scottish government announced that travellers arriving from Portugal will have to be in isolation for two weeks from 4am on 5 September, joining Wales, which had already determined the same measure from 4am on 4 Septmber.
"This week's data show an increase in positive tests and cases per 100,000 inhabitants in Portugal," justified Scottish Justice Minister Humza Yousaf.
The announcement comes two hours after Welsh Health Minister Vaughan Gething removed mainland Portugal from the list of countries and territories free of quarantine, but keeping the Azores and Madeira.
The Welsh government also decided to exclude Gibraltar, and six Greek islands (Mykonos, Zakynthos, Lesvos, Paros and Antiparos and Crete) from the list of safe territories.
Scotland had already decided to impose quarantine on the whole of Greece since 3 September and Yousaf left the warning that Gibraltar is at the top of the list of destinations under surveillance.
In the afternoon, British Transport Minister Grant Shapps had said that Portugal and Greece were still on England's list of safe countries, despite speculation that they would be withdrawn.
"We continue to keep the list of travel corridors under constant review and will not hesitate to remove countries if necessary. However, there are no additions or removals today," he announced through the social media platform Twitter.
However, he added, "tourists are reminded - countries with 14-day quarantine can and do change at very short notice.”
The British government's decision applies only to England, since the other nations of the United Kingdom have autonomy in this matter.
Northern Ireland has also not announced any change, remaining in line with London's guidelines.
Portugal was only included in the list of countries with "travel corridors" with the United Kingdom two weeks ago, on 20 August, despite pressure from the Portuguese government and the tourism sector on the British authorities.
The decision to add or remove a country is made after an analysis of the Common Biosafety Centre, which uses as its main indicator the level of 20 cases per 100,000 inhabitants in seven days, but also takes into account other factors such as prevalence, level, rate of change of confirmed positive cases.
Initially done every three weeks, the reevaluation of the measures is now done weekly.